The invention generally relates to hydrostatic supporting devices, hydrostatic buttons, and in particular to hydrostatic buttons for supporting the axial thrust movement of a rotating collared shaft.
Hydrostatic buttons in various forms are already known and disclosed in U.S. Patent to: Christ et al U.S. Pat. No. 4,073,549, Engel et al U.S. Pat. No. 3,635,126, Van Gaasbet et al U.S. Pat. No. 3,799,628 and Spillman et al U.S. Pat. No. 3,802,044.
Hydrostatic buttoms comprise a top cylindrical head portion, having a bearing face operationally in supportive contact with a collared shaft bearing face, and a bottom cylindrical skirt portion. The skirt portion is provided with a circumferential groove, on its outer cylindrical surface, for receiving an elastomeric o-ring seal. The button is centrally bored along its symmetric axis and provided with an orifice therein. The button top cylindrical head portion includes a central circular recess, oriented coaxial with the button central bore, which is in fluid communication with the button central bore. Individual buttons are supported from a cooperating foundation in a cylindrical pocket therein, which pocket is fed pressurized fluid through a connecting passage in fluid communication with a pressurized fluid source. Typically a plurality of buttons are arranged in a circular array about the axis of the collared shaft. The o-ring seal prevents pressurized fluid from leaking from the pocket along the outer cylindrical surface of the skirt, thus creating a servomotor. The o-ring also provides some radial support for the button.
In operation, fluid pressure in the servomotor urges the hydrostatic button in the direction of the bearing face of the collared shaft. Pressurized fluid is bled through the button's orificed central bore to the central circular recess. Thus a hydrostatic bearing is formed capable of resisting thrust loading from a collard shaft bearing face tending to move the hydrostatic button toward the foundation pocket.
Since the collared shaft bearing face is rotating, there is some hydrodynamic bearing effect along with the hydrostatic bearing formed by the flow of pressurized fluid over the bearing face of the hydrostatic button. Rotation of the collar shaft tends to increase the flow of the pressurized fluid passing over the trailing edge of the hydrostatic button bearing face and results in a slight tip or tilt of the button.
While some tilting of the hydrostatic button is tolerable, the button must be constructed in a manner to avoid significant non-parallelism between the button bearing face and the bearing face of the shaft collar if this particular type of thrust compensation is to be effectively employed. The consequence encountered if significant non-parallelism occurs is gouges or nicks in the collared shaft bearing surface and eventual bearing failure.
To avoid significant non-parallelism some artisans have attempted to force balance the design of the hydrostatic button bearing face to avoid the adverse hydrodynamic bearing effects causing the tilting of the button. This approach results in very tight machining tolerances and significant expense, but is necessary due to the ineffectiveness of the o-ring to provide adequate radial support.
Furthermore the o-ring also tends to extrude into the circumferential groove as the button reciprocates causing a high and unconstant resistance to the button's travel.